Many materials and products are produced most efficiently in large quantities or, in the case of farm grain products, must be produced all at once due to environmental factors. In order to realize some of the benefits of efficient production, these materials must be conveniently and inexpensively stored until they are needed. The current practice involves the use of bulk storage buildings; however, there are several significant drawbacks to these buildings. Generally speaking, the larger the storage building, the more cost-efficient it becomes; however, a major problem involves the tremendous downward and lateral pressures exerted on the walls of the storage building by the materials placed inside. When a semi-fluid material such as clay particles or grain is poured into a storage facility from the top, or even when poured on the ground, it forms a cone, with the angle between the sides of the cone and the base forming the angle of repose of the material. This configuration, with the weight concentrated at the bottom and sides of the cone, along with the friction exerted downwardly on the wall of the building by the material inside, accounts for the high pressures. For example, a circular storage building of relatively modest size having a diameter of 16 feet and a height of 20 feet will hold approximately 3220 bushels of small-particle grain. This quantity exerts forces on the side walls of 2000 pounds downward pressure per lineal foot and 400 pounds lateral pressure per square foot. Similar values are obtained for other small-particle products such as dried clay. Since building sizes may extend to capacities over 10,000 bushels, the pressures exerted on the building are of primary concern. Reinforcement measures taken to insure the integrity of the structures add substantially to their costs, requiring users to strike a balance between storage capacity needed and the cost of a structure which is able to withstand the large pressures involved.
One of the main reasons for having storage facilities is to keep the stored materials out of the weather; however, ventilation is desirable to prevent spoilage or to effect further drying once the material is stored. For example, dried clay is used in many instances as an absorbent and its chief economic value lies in the dryness of the material; thus, shelter is essential. Most grains must be dried before storage to an approximate moisture content ranging from 12% to 14% lest spoilage occur, and once the products have been dried, often using expensive drying equipment, they must be kept dry to avoid losses from spoilage, from having to sell damp grain with its concomitant lower price, or from having to re-dry the materials. However, slight declines in moisture content are acceptable in many cases, and since spoilage can occur where the grain has not been dried to its optimum moisture content, ventilation is normally desired; thus, the structure must serve both interests.
Bulk storage also confers benefits on users where a large quantity of material must be stored in order to maintain adequate supplies for use over a period of time, as with road salt and sand stored for use over the winter. Fewer deliveries and fewer storage facilities translate into greatly reduced costs, thus freeing funds for purchase of additional stored materials instead of for additional storage facilities, more deliveries, and/or reinforcement of existing structures.